Electronic control of a vehicle-mounted device such as an engine of the vehicle with an electronic control apparatus is increasingly taking place. For example, an engine ECU (Electronic Control Unit) calculates a fuel injection amount, fuel injection timing, a throttle opening rate, etc., to control the corresponding actuators. Such an electronic trend helps to achieve improvement in response to a driver's operation and fuel savings.
However, such an electronic trend tends to induce an increase in the number of tasks to be executed by one electronic control apparatus. Further, there is such a tendency that the higher the engine rpm is, the shorter the control cycle of the electronic control apparatus becomes. Thus, if the engine rpm is high, all the tasks may not be completed within a given time (this phenomenon is referred to as one of a task omission). For this reason, the electronic control apparatus sets priority of the tasks and may execute the tasks such that the task with higher priority is executed before the task with lower priority (see Patent Document 1, for example). Patent Document 1 discloses a failure detector configured such that the task with higher priority is executed with reliability in a predetermined interval while it is permitted that the task with lower priority is not executed in the predetermined interval.
However, if it is permitted that the task with lower priority is not executed as disclosed in Patent Document 1, high frequency of these permissions causes reduced drivability. Further, it is preferred that the task omission is prevented in order to optimize traveling control.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2009-116816